ops: add nix.yml

Author: es-sai-fi

.github/workflows/nix.yml

@@ -0,0 +1,18 @@
+name: Nix Build and Flake Check
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["*"]
+
+jobs:
+  nix:
+    runs-on: ubuntu-latest
+
+    steps:   
+      - uses: actions/checkout@v6
+      - name: Install nix
+        uses: cachix/install-nix-action@v31
+      - name: Check flake
+        run: nix flake check